More changes for registry-v2 in python.

Implement the minimal changes to the local filesystem storage driver and feed them through the distributed storage driver.
Create a digest package which contains digest_tools and checksums.
Fix the tests to use the new v1 endpoint locations.
Fix repository.delete_instance to properly filter the generated queries to avoid most subquery deletes, but still generate them when not explicitly filtered.

storage/basestorage.py

@@ -93,3 +93,28 @@ class BaseStorage(StoragePaths):
 
   def get_checksum(self, path):
     raise NotImplementedError
+
+
+class DigestInvalidException(RuntimeError):
+  pass
+
+
+class BaseStorageV2(BaseStorage):
+  def initiate_chunked_upload(self):
+    """ Start a new chunked upload, and return a handle with which the upload can be referenced.
+    """
+    raise NotImplementedError
+
+  def stream_upload_chunk(self, uuid, offset, length, in_fp):
+    """ Upload the specified amount of data from the given file pointer to the chunked destination
+        specified, starting at the given offset. Returns the number of bytes written.
+    """
+    raise NotImplementedError
+
+  def complete_chunked_upload(self, uuid, final_path, digest_to_verify):
+    """ Complete the chunked upload and store the final results in the path indicated.
+    """
+    raise NotImplementedError
+
+
+